Muscle structure neuromuscular junction

According to Fig. 6.17 the nerve cell is linked to other excitable, both nerve and muscle, cells by structures called, in the case of other nerve cells, as partners, synapses, and in the case of striated muscle cells, motor end-plates neuromuscular junctions). The impulse, which is originally electric, is transformed into a chemical stimulus and again into an electrical impulse. The opening and closing of ion-selective channels present in these junctions depend on either electric or chemical actions. The substances that are active in the latter case are called neurotransmitters. A very important member of this family is acetylcholine which is transferred to the cell that receives the signal across the postsynaptic membrane or motor endplate through a... 

Succinylcholine acts primarily at the skeletal neuromuscular junction and has little effect at autonomic ganglia or at postganglionic cholinergic (muscarinic) junctions. Actions at these sites attributed to succinylcholine may arise from the effects of choline. Succinylcholine has no direct action on the uterus or other smooth muscle structures. It does not enter the CNS and does not cross the placental barrier. It may, however, release histamine from mast cells. Because succinylcholine works by stimulating rather than blocking end plate receptors, anti-AChEs will not reverse muscle paralysis and may actually prolong the block. 

At the neuromuscular junction, it produces the contraction of skeletal muscle by its direct action and by inactivation of anticholinesterase and has got anticurare action. By virtue of its structural similarity to acetylcholine, it acts as partial agonist on motor end plate. 

Aldridge and Reiner 1972). The A esterases have a serine catalytic site. The tertiary structure and amino acid sequences of several AChEs and BuChEs have been established (Taylor 1994). AChEs regulate excitation at cholinergic synapses, destroying the neurotransmitter ACh. AChE is one of the most active enzymes known, cycling within a few milliseconds (Taylor 1996). AChEs are found at synapses and neuromuscular junctions, and in central-nervous-system (CNS) neuron cell bodies, axons, muscles, red blood cells (RBCs), and platelets of ovine and rodent species (Silver 1974 Traina and Serpietri 1984 Hoffmann et al. 1989). 

Askanas, V., Kwan, H., Alvarez, R.B., Engel, W.K., Kobayashi, T., Martinuzzi, A., Hawkins, E.F. (1987). De novo neuromuscular junction formation on human muscle fibres cultured in monolayer and innervated by foetal rat spinal cord ulfra-structural and ultrastmctural-cytochemical studies. J. Neuro-cytol 16 523-37. 

Muscarine binds to the so-called muscarinic receptors in the parasympathetic nervous system. These are primarily postganglionic cholinergic receptors in smooth muscle and glands. Muscarine does not act on so-called nicotinic receptors, which are found in ganglionic synapses and at the neuromuscular junction. Muscarine is a tertiary amine structure and, therefore, does not diffuse into the central nervous system to an appreciable extent. Symptoms are, therefore, limited to the peripheral nervous system. 

Fig. 11.2. Acetylcholine receptors at the neuromuscular junction. A motor nerve terminates in several branches each branch terminates in a bulb-shaped structure called the presynaptic bouton. Each bouton synapses with a region of the muscle fiber containing junctional folds. At the crest of each fold, there is a high concentration of acetylcholine receptors, which are gated ion channels.

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